Pneumatic tires

ABSTRACT

A pneumatic tire comprises a carcass comprised of at least one carcass ply containing a steel cord(s) arranged at a cord angle of 70-90° with respect to an equatorial plane of the tire and toroidally extending between a pair of bead cores and turned up around the bead core inward or outward in a radial direction to form a turnup portion, wherein a wrap part wrapping on a peripheral face of the bead core therealong is formed in the turnup portion of the carcass ply.

This is a divisional of application Ser. No. 09/493,116 filed Jan. 28,2000, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a pneumatic tire, and more particularly to animprovement of a bead portion structure in a heavy duty pneumatic radialtire capable of effectively preventing the pulling-out of carcass plycord, occurrence of separation failure at turnup portion of carcass plyand the like to improve the durability. Further, it relates to a methodof manufacturing such a pneumatic tire as well as a carcass band bendingapparatus used therefor and a tire manufacturing apparatus.

2. Description of Related Art

In the conventional heavy duty pneumatic radial tire, the carcass ply istoroidally extended between a pair of bead cores in bead portions andturned up around the bead core from an inside of the tire toward anoutside thereof in a radial direction and the resulting turnup portionis embedded and fixed in rubber in order to prevent the pulling-out ofthe carcass ply cord during the running of the tire under loading.

FIGS. 1a and 1 b show diagrammatically section views of typicalembodiments of the bead portion in the conventional heavy duty pneumaticradial tire, respectively. In the illustrated embodiment of FIG. 1a, anouter end of a turnup portion 1 a of a carcass ply 1 wound around a beadcore 3 is located outward from an outer end of a wire chafer 2 in aradial direction of the tire. In the illustrated embodiment of FIG. 1b,the outer end of the wire chafer 2 is located outward from the outer endof the turnup portion 1 a of the carcass ply 1 in the radial direction.Moreover, numeral 4 is a bead filler.

In such conventional bead portion structures, however, the difference ofstiffness is produced between inside and outside in the radial directionof the tire on the border of the position of the outer turnup end of thecarcass ply 1 or the outer end of the wire chafer 2, a zone ranging fromthe bead portion to the sidewall portion is subjected to repetitivedeformation during the running of the tire under loading, whereby stressis concentrated at each of the outer ends and in the vicinity thereofand hence it is apt to cause separation failure at the outer end fromrubber, which results in the occurrence of crack cr in the bead portionas shown in FIGS. 2a and 2 b.

In order to mitigate stress produced at the outer turnup end of thecarcass ply 1 or the outer end of the wire chafer 2 and in the vicinitythereof and enhance the stiffness of the bead portion to control thedeformation of the bead portion, therefore, there are proposed a methodwherein plural organic fiber cord layers (not shown) are circumscribedwith the wire chafer 2 around the bead core 3 so as to cover the outerturnup end of the carcass ply 1 or the outer end of the wire chafer 2, amethod of increasing an amount of the bead filler 4, particularly hardrubber filler arranged at the outside of the bead core 3 between a mainbody of the carcass ply 1 and the turnup portion thereof in the radialdirection, and the like. According to these methods, however, the heatgenerating temperature of the bead portion becomes more higher duringthe running of the tire under loading, which results in the occurrenceof separation failure even at the outer end of the organic fiber cordlayer in addition to the above separation failure, and also the tireweight is undesirably increased to lower the productivity of the tire.

When the heavy duty pneumatic radial tire is used several times byrecapping after the wearing, there is a further problem that it isimpossible to use the tire due to the occurrence of separation failurearound the turnup end of the carcass ply subjected to stressconcentration in the use over a long time.

As a countermeasure for solving such a problem, there is a techniquethat the rubber gauge of the bead portion is reduced by forming a recessportion in an outer profile of the bead portion at the radial section ofthe tire to lower the heat build-up of the bead portion (for example,JP-A-57-191104). In this technique, however, the rubber gauge of thebead portion can not be reduced too much owing to the presence of theturnup portion of the carcass ply, so that the effect of improving thebead portion durability can not be said to be sufficient.

Furthermore, JP-A-10-193924 proposes a technique that the thickness ofthe bead portion is decreased by extending the turnup portion along themain body of the carcass ply to form a recess portion in the outerprofile of the bead portion. In this case, however, shearing strain iscaused in an interface between the main body and the turnup portion ofthe carcass ply is increased by the shearing deformation based on thepushing from the rim flange under loading as the rubber gauge at theoutside of the turnup portion is decreased and hence there is caused aproblem that separation failure is caused between the carcass ply andrubber located at the outside thereof.

In any case, it is insufficient to prevent the separation failure in thebead portion even by these conventional techniques because the serviceconditions of the large-size pneumatic radial tire become recentlyseverer with the increase of the recapping number from viewpoints ofenvironmental consideration and economical merit and the bead portiondurability is degraded in lower section-profile tires recently used, andhence basic solution for bead portion troubles are not yet obtained.

In the manufacture of the tire as mentioned above, when the winding ofthe turnup portion of the carcass ply around the peripheral surface ofthe bead core is carried out by subjecting the ply cords and hence thecarcass ply to elastic deformation in the winding direction with, forexample, well-known bladder, blade, roll and the like and then stickingthe elastic deformed turnup portion onto the peripheral surface of thebead core with rubber, it is difficult to wind the ply cords onto theperipheral surface of the bead core with a high accuracy as is expected.And also, ply cords having a large elastic restoring force such as steelcords, aromatic polyamide cords and so on can not accurately bemaintained at the required winding position irrespectively of the plycord having a small elastic restoring force. In any case, there is aproblem that the pulling-out of the ply cord and the separation failureat the turnup end of the carcass ply can not sufficiently be prevented,respectively.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to solve the aforementionedproblems of the conventional techniques and to provide pneumatic tired,particularly heavy duty pneumatic radial tires capable of effectivelypreventing the separation failure at outer ends of the carcass ply andwire chafer from rubber and the pulling-out of the carcass ply cord tolargely improve the bead portion durability without the increase of thetire weight, the degradation of the tire productivity and the like.

It is another object of the invention to provide a method for themanufacture of the pneumatic tire capable of accurately winding theturnup portion of the carcass ply onto the peripheral surface of thebead core as is expected and surely maintaining the wound posture evenwhen using the ply cord having a large elastic restoring force as wellas a carcass band bending apparatus used therefor and a tiremanufacturing apparatus.

According to a first aspect of the invention, there is the provision ofin a pneumatic tire comprising a carcass comprised of at least onecarcass ply containing a steel cord(s) arranged at a cord angle of70-90° with respect to an equatorial plane of the tire and toroidallyextending between a pair of bead cores and turned up around the beadcore inward or outward in a radial direction to form a turnup portion,the improvement wherein a wrap part wrapping on a peripheral face of thebead core therealong is formed in the turnup portion of the carcass ply.

In the invention, there are a case that the turnup portion is formed bywinding the carcass ply from an inside toward an outside in a widthwisedirection of the tire, and a case that the turnup portion is formed bywinding the carcass ply from an outside toward an inside in thewidthwise direction of the tire.

And also, the carcass ply includes a case that many steel cords aresubstantially radially arranged side by side, and a case that a singlesteel cord is turned at a position corresponding to the turnup portionof the carcass ply and extended at a detoured state in thecircumferential direction of the tire.

In the pneumatic tire according to the invention, the wrap part wrappingalong the peripheral face of the bead core is formed in the turnupportion of the carcass ply, whereby the pulling-out of the carcass plycord can effectively be prevented without prolonging the turnup portionoutward in the radial direction of the tire. And also, the wrap part islocated sufficiently adjacent to the bead core having a high stiffness,so that the deformation of a zone in the vicinity of the wrap partduring the running of the tire under loading is effectively restrainedby the bead core, a rim supporting the bead portion and the like. As aresult, there is no fear of concentrating stress in the wrap part andits neighborhood due to the above deformation and hence separationfailure at the wrap part and hence the turn up portion is effectivelyprevented.

In such a tire, at least one plastic deformation region is formed in thewrap part. Such a plastic deformation region can be realized, forexample, by providing the wrap part with at least one bent or formedzone of rectangle, curve or the like adaptable to a radially sectionalprofile shape of the bead core. Since the wrap part is located nearer tothe peripheral face of the bead core and more accurately followedthereto by the plastic deformation region, the wrap part can moreeffectively be restrained by the bead core to further effectivelyprevent the pulling-out of the carcass ply cord and separation failureof the turnup portion.

The plastic deformation region is preferable to be previously formed ina portion of the carcass ply corresponding to the warp part prior to thewinding of the carcass ply around the bead core. Thus, the plasticdeformation can always and accurately be conducted as it is expected andhence the above effect can be more enhanced.

In a preferable embodiment of the first aspect of the invention, atleast the wrap part of the turnup portion is interposed between the beadcore and a bead filler, whereby the wrap part can be closed to the beadcore through the bead filler to more advantageously prevent thepulling-out of the carcass ply cord and separation failure of the wrappart.

In another preferable embodiment of the first aspect of the invention,the wrap part is extended along the peripheral face of the bead coreover a half periphery of the sectional profile of the bead core. Ingeneral, the bead core has a polygonal shape, a circular shape or thelike as the radially sectional profile. In any shapes, theaforementioned effect can be more enhanced by extending the wrap partalong the bead core over the half periphery of the sectional profile.

In the other preferable embodiment of the first aspect of the invention,an outer end of the turnup portion is located inward from an outercircumferential edge of the bead portion at the contact region with therim flange in the radial direction of the tire. The term “contact regionof the bead portion with the rim flange” used herein means a maximumcontact region of the bead portion with the rim flange during therunning of the tire at a maximum air pressure under a maximum load.

Thus, when the turnup portion has an outer end region protruding outwardfrom the end of the wrap part in the radial direction, the outer end isstrongly held by the rim and can be located in a zone having a verylittle deformation during the running of the tire under loading, wherebythe concentration of stress in the outer end and the neighborhoodthereof can effectively be prevented to sufficiently protect the outerend region of the turnup portion against the separation failure.

Particularly, this becomes conspicuous when the end of the wrap part islocated inside in the radial direction over a position corresponding toan outer peripheral edge of the bead core embedded in the bead portionat a state of mounting onto the rim in the inflation under the maximumair pressure so as to make longer than a length of the wrap part alongthe bead core.

Moreover, the above features are particularly-effective in pneumatictires having an aspect ratio of not more than 60%. That is, in the tirehaving a small aspect ratio, shearing strain in the circumferentialdirection occupies a large weight rather than compression strainproduced in the turnup end of the carcass ply due to the occurrence ofinternal stress accompanied with the bending deformation of the sidewallportion during the running of the tire under loading as a cause ofcreating separation failure of the turnup portion, but in the tireaccording to the invention, the turnup portion is wrapped so as tolocate an end of the wrap part in the vicinity of the bead core having aless deformation, whereby the end of the turnup portion is workedtogether with the main body of the carcass ply and hence shearing strainin the circumferential direction to road surface can advantageously bereduced.

In the first aspect of the invention, it is favorable that the steelcord as the carcass ply cord has a tenacity of 80-300 kgf, preferably100-180 kgf. When the tenacity is less than 80 kgf, it is difficult toensure a given tenacity when the carcass ply cord is subjected toplastic deformation to decrease the tenacity by about 10-20%, while whenit exceeds 300 kgf, the diameter of the cord becomes too thick and theplastic deformation becomes difficult and it is apt to create injury inthe cord through the plastic deformation.

Even in the above tire, it is sometimes apt to cause a permanent set infatigue of the bead portion, which may cause the cracking at the outsideof the bead portion in the recapping or separation failure at a chafermember and hence the bead portion durability may not sufficiently beimproved.

Therefore, the inventors have considered that the permanent set of thebead portion can be controlled by taking means for reducing a contactpressure between the bead portion of the tire and the rim when the tireis changed from deflate state to an inflate state and made variousstudies. As a result, it has been confirmed that the change of a profileof a carcass line located in a region of the bead portion outward from acontact region with a rim flange in the radial direction of the tire ismade small when the tire is changed from the deflate state to theinflate state, and particularly the amount of pushing out the beadportion toward the rim flange is made small, and more concretely adisplacement (d) of a point X changed from a deflate state to an inflatestate is not more than 3 mm as measured at a section in the widthwisedirection of the tire, wherein X is an arbitrary point on a carcass linelocated in a region of the bead portion outward from a contact regionwith a rim flange at the deflate state when the tire is mounted onto arecommended rim, whereby the contact pressure with the rim flange can bemade small to considerably decrease the permanent set of the beadportion.

The position of the point X means an arbitrary point located on thecarcass line within a range of ±20 mm centering on an intersect betweenthe carcass line and a normal line drawn from the contact point with therim flange to the carcass line at the deflate state of the tire. Inother words, the point X existing within the above range means that thedisplacement d is not more than 3 mm.

And also, the displacement d means a displacing amount when the point Xon the carcass line at the deflate state moves to a point X′ at aninflate state (distance between point X and point X′).

The term “deflate state” used herein means that the tire is at aself-supportable state on the rim under no load after air is dischargedfrom the inside of the tire or concretely at a state under an airpressure of 0.5-1.0 kgf/cm². And also, the term “inflate state” usedherein means that the tire is at a state of inflating at an air pressurecorresponding to a maximum air pressure under no load.

Further, the term “maximum air pressure” used herein means an airpressure corresponding to a maximum load of a single wheel having anapproved size described in the following standard (maximum loadcapacity), and the term “recommended rim” used herein means arecommended rim (or approved rim) described in the following standard.

The standard is defined by Year Book of The Tire and Rim AssociationInc. in USA, Standard Manual of The European Tire and Rim TechnicalOrganization in Europe, and Year Book of JATMA in Japan, respectively.

Moreover, the term “carcass line” used herein means a line passingthrough a thickness center of the carcass ply constituting the carcassbody at a section of the tire in the widthwise direction. Concretely,when the carcass body is comprised of one ply, the carcass line is aline passing through the center of the cord embedded in the ply, whilewhen the carcass body is comprised of two or more plies, the carcassline is a line passing through a thickness center of the laminatedplies.

In FIG. 3 is shown an example of results measured on contact pressure tothe rim flange in tires having different displacements d (i.e.pushing-out amount of bead portion) when the tire is changed from thedeflate state to the inflate state.

As seen from FIG. 3, when the displacement d exceeds 3 mm, the contactpressure rapidly increases. In the usual tire, the displacement d at theinflate state is generally within a range of 4-6 mm.

In order to decrease the displacement d, it is favorable to satisfy arelation of R₀<2H, preferably R₀<H when a radius of curvature of thecarcass line at the point X is R₀ and a section height of the tire is Hat the deflate state.

In case of R₀<H, the pushing-out amount of the bead portion can be zeroor the bead portion can be deformed (recessed) in a direction oppositeto the pushing-out direction, whereby the contact pressure to the rimflange can be more reduced.

In a still further preferable embodiment of the first aspect of theinvention, a rubber layer controlling shearing strain is arrangedbetween a bead filler and a bead portion reinforcing layer located at anoutside of the tire, whereby shearing strain is suppressed at the turnupend portion of the carcass ply.

In this case, the rubber layer has a hardness middle between hardness ofthe bead filler and hardness of a sidewall rubber constituting asidewall portion together with the bead filler. And also, a ratio of thehardness of the bead filler to the hardness of the sidewall rubber isnot less than 1.4 times. Thus, the difference of stiffness between thebead filler and the sidewall rubber can be made small and alsoexcessively interlaminar shearing strain is suppressed between therubber layer and the bead portion reinforcing layer to avoid theoccurrence of separation failure from an end portion of the bead portionreinforcing layer. Moreover, even when the number of the reinforcinglayers is increased for preventing the deformation in the bead portion,stress does not concentrate in the vicinity of the end of such areinforcing layer, so that the shearing strain resulting in theoccurrence of separation failure is decreased.

When the thickness of the rubber layer is t₂ and the thickness of thebead portion reinforcing layer is t_(l), it is favorable to satisfy arelation of 0.3t₁<t₂≦5t₁. Thus, the deformation of the bead portion canbe prevented without the concentration of shearing strain in the endportion of the bead portion reinforcing layer.

Furthermore, it is favorable that an end of the rubber layer is locatedat a position corresponding to an upper part of the bead core,preferably so as to contact with the turnup portion of the carcass plyand the other end thereof is extended along the bead portion reinforcinglayer and protruded from an end of the reinforcing layer by 30 mm atmaximum. Thus, it is possible to avoid the concentration of shearingstrain in the turnup end of the carcass ply and the end of thereinforcing layer.

In the other preferable embodiment of the first aspect of the invention,a recess zone is formed in an outer profile of the bead portion locatedinward from a position of a maximum tire width in the radial directionof the tire at a radial section of the tire. Thus, the heat build-up ofthe bead portion during the running of the tire under loading isdecreased by the formation of the recess zone, whereby the bead portiondurability can be largely improved.

In the tire having the recess zone in its bead portion, a rubber gaugein a region ranging outward from a position corresponding to 1.8 times amaximum bead portion width located from a position of a nominal diameterof a rim flange in the radial direction of the tire to the position ofthe maximum tire width is substantially equal to a rubber gauge at theposition of the maximum tire width. That is, the rubber gauge T(distance from the cord in the carcass ply to the outer profile of thetire) in a region ranging outward from a position corresponding to 1.8times the maximum bead portion width located from the position of thenominal diameter of the rim flange in the radial direction of the tireto the position of the maximum tire width (rubber located at the outsideof the carcass ply) is made substantially equal to the rubber gauge atthe position of the maximum tire width (0.7-1.3 times the thickness atthe position of the maximum tire width), while the rubber gauge in aregion ranging inward from the position corresponding to 1.8 times themaximum bead portion width in the radial direction of the tire to aposition of the bead core is gradually increased (or the depth of therecess zone is gradually decreased).

In general, the sidewall rubber is enough to have a rubber gaugerequired for preventing external injury in the vicinity of the positionof the maximum tire width and is set to a value of rubber gauge thinnerthan that in the bead portion or the like. Even in the bead portion, itis desirable to make the rubber gauge thin considering only the heatbuild-up. On the other hand, the bead core is necessary to have acertain stiffness for fixing the tire onto the rim. If the rubber gaugeis made thin up to the vicinity of the bead core likewise the case atthe position of the maximum tire width, the bending deformation of thebead portion concentrates in the vicinity of the bead core to cause theconcentration of strain in the rubber of the bead portion near to thebead core and hence there is caused a problem that crack is created atthe outer surface of the tire in the vicinity of the bead core. However,such a problem is solved by the relation of rubber gauge as mentionedabove in the invention.

Furthermore, it is favorable that the recess zone is arranged outwardfrom an alienation point between the outer surface of the bead portionand the rim flange in the radial direction of the tire when the tire ismounted onto a recommended rim and stated at a maximum air pressureunder a maximum load. If the recess zone is formed in a region of thebead portion contacting with the rim flange under loading, an amount ofa space between the outer surface of the bead portion and the rim flangeunder an inflation of the air pressure is increased to increase theamount of the bending deformation under loading in the vicinity of sucha region, which badly affects the bead portion durability. This problemis solved by arranging the recess zone outward from the alienation pointbetween the outer surface of the bead portion and the rim flange underloading in the radial direction as mentioned above.

Moreover, when the width of the bead portion is violently decreased ascompared with the maximum bead portion width in the region contactingwith the rim flange under loading, the amount of space between the outersurface of the bead portion and the rim flange increases to increase thefall-down deformation of the bead portion. For this end, it is favorablethat a thickness W_(P) of the bead portion at the alienation point Pbetween the outer surface of the bead portion and the rim flange at theinflation state of the maximum air pressure under the maximum load afterthe mounting onto the recommended rim satisfies a relation ofW_(P)/W_(M)≧0.9 when a width of the bead portion passing through aillustrated center of the bead core in parallel to a standard line ofthe bead portion thickness at the alienation point P is W_(M).

According to a second aspect of the invention, there is the provision ofa method of manufacturing a pneumatic tire, which comprises subjecting acylindrical carcass band to a forming treatment by bending each endportion of the band in at least one place in an axial direction of agreen tire over a full circumference thereof inward or outward in aradial direction of the tire, arranging a ring-shaped bead core on aninside of the bent end portion, toroidally expanding the cylindricalcarcass band while locking the bead core, and then joining a belt and atread onto an outer peripheral side of the carcass band.

According to this method, the previously formed bent end portion isaccurately formed in the required position of the cylindrical carcassband in correspondence with the peripheral shape and dimension of thebead core and then the bead core is inserted into the inside of the bentend portion, whereby the bent end portion can accurately be wound aroundthe peripheral surface of the bead core even when the ply cord has alarge elastic restoring force as in steel cord. And also, the windingposture can surely be maintained based on the plastic deformationthrough the previous forming, so that the fear of pulling-out the plycords is sufficiently removed and also the separation failure of theturnup portion of the carcass ply from rubber can always and surely beprevented.

The bending formation of the end portion of the carcass band can be madeinward or outward in the radial direction of the carcass band. In theformer case, the end portion of the carcass band is turned up around thebead core from outside toward inside in the widthwise direction of thetire in a product tire. In the latter case, the end portion is turned upfrom inside toward outside in the widthwise direction of the tire.

Moreover, when there are plural bending positions in this method, theoperation of the bending formation is carried out by bending each endportion of the cylindrical carcass band simultaneously at pluralpositions in the axial direction or in a given order. The simultaneousbending at plural positions is advantageous in view of the operationefficiency unless one of the positions affects the other position and isobstructed by the other position.

In a preferable embodiment of the second aspect of the invention, thebending at the each end portion of the cylindrical carcass band iscarried out by relatively displacing a bending means and a cylindricalcarcass band in the circumferential direction of the cylindrical carcassband. In this case, a bending means relatively displacing to acircumferential direction of a carcass band drum and hence acircumferential direction of a cylindrical shaped carcass band formed onthe drum is merely added on the existing carcass band drum, and thecylindrical carcass band is subjected to the required bending work byputting the cylindrical carcass band from inner and outercircumferential sides thereof through the bending means, whereby thebent portion can surely be formed in the cylindrical carcass band beingstructurally soft with a less equipment cost as is expected.

In another preferable embodiment of the second aspect of the invention,the arrangement of the bead core at the inside of the bent end portionis carried out by subjecting the bent end portion to elastic deformationin an opening direction. When the cross sectional shape of the bent endportion is polygonal or the like and it is impossible to insert the beadcore into the inside of the bent end portion at a state of bentformation, the insertion of the bead core is carried out at a state ofopen-deforming at an elastic zone, whereby the bead core can accuratelybe arranged in the required position and hence the proper winding of thebent end portion around the peripheral surface of the bead core cansurely be realized.

In the other preferable embodiment of the second aspect of theinvention, the bend end portion is subjected to stitching at a state oftoroidally expanding the cylindrical carcass band while locking the beadcore. In this case, the bend end portion can sufficiently be pressedonto the peripheral surface of the bead core by the stitching togetherwith the pushing of air from both members at a state of sufficientlyapproaching the extending form of the carcass band to that of the greentire, whereby the expected effect can be more enhanced.

The bending formation of the end portion in the cylindrical carcass bandcan naturally be carried out even when the carcass band is comprised oforganic fiber cords having a large elastic restoring force such asaromatic polyamide cords and the like, but the plastic deformation forthe required bending formation can be carried out with a more higheraccuracy when the carcass band is comprised of steel cords. And also, itis advantageous to develop the higher cord tenacity even when theplastic deformation is carried out.

According to a third aspect of the invention, there is the provision ofan apparatus for bending a carcass band for use in the manufacture ofthe pneumatic tire, comprising a shaft-shaped member provided with anannular groove supporting an end portion of a cylindrical carcass bandfrom an inner or outer circumferential side thereof, and a disc-shapedmember located in a position corresponding to the annular groove andpushing the cylindrical carcass band into the annular groove.

In this bending apparatus, the cylindrical carcass band is puttedbetween the shaft-shaped member and the disc-shaped member and pushedinto the annular groove at a given force, so that the bending formationcan simply, easily and accurately be carried out at a required positionof the cylindrical carcass band in its axial direction by a simple andsmall apparatus independently separated from a carcass band drum formingthe cylindrical carcass band. Such a bending formation can properly becarried out over a full circumference of the carcass band having a softstructure without disturbing the cord arrangement or the like in thecarcass band, for example, by rotating at least one of the shaft-shapedmember and the disc-shaped member to relatively move the bendingapparatus to the cylindrical carcass band in the circumferentialdirection thereof, or by rotating the cylindrical carcass band to thebending apparatus.

In such a bending apparatus, when a plurality of annular grooves areformed on the shaft-shaped member at given intervals and disc-shapedmembers in accordance with the number of the annular grooves arearranged side by side in the same axial line, the bending formation cansimultaneously be carried out in plural positions of the cylindricalcarcass band separated at given intervals in its axial direction by theone action of the apparatus, whereby the working efficiency can largelybe increased.

Moreover, the relative movement between the bending apparatus and thecylindrical carcass band in the circumferential direction can be carriedout by connecting at least one of the cylindrical carcass band,shaft-shaped member and disc-shaped member to a rotation driving means,or by rotating at least one of the shaft-shaped member and thedisc-shaped member on its axis and arranging a driving means forrevolving both the members around the circumference of the cylindricalcarcass band.

According to a fourth aspect of the invention, there is the provision ofan apparatus for manufacturing a pneumatic tire, comprising a carcassband drum forming a cylindrical carcass band, a carcass band bendingapparatus for subjecting an end portion of the cylindrical carcass bandlocated on the carcass band drum to bending formation, a bead setter forarranging a ring-shaped bead core inside the bent end portion of thecylindrical carcass band, a bead lock for supporting the bead corearranged on the bend end portion from its inner peripheral side, and ashaping means for toroidally expanding the cylindrical carcass band.

According to this manufacturing apparatus, the above manufacturingmethod can easily be realized by adding the carcass band bendingapparatus to the existing tire building apparatus, somewhat improvingthe bead setter and the like.

In this case, the shaping means can be added to the carcass band drum.Thus, the installation cost can be controlled to a low level bydecreasing the number of the drums and also the step of transporting thecylindrical carcass band or the like can be made useless.

Alternatively, the shaping drum provided with the shaping means isdisposed irrespectively of the carcass band drum and a transportationmeans for transporting the formed cylindrical carcass band into theshaping drum, and the carcass band bending apparatus and the bead settercan be added to the transportation means.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein:

FIGS. 1a and 1 b are diagrammatically partial section views illustratingembodiments of a bead portion structure in the conventional tire;

FIGS. 2a and 2 b are diagrammatically partial section views illustratingthe occurrence of crack in the bead portion shown in FIGS. 1a and 1 b;

FIG. 3 is a graph showing a relation between a displacement d of a pointX on a carcass line when a tire is changed from a deflate state to aninflate state and a contact pressure to a rim flange;

FIG. 4 is a diagrammatically left-half section view of a firstembodiment of the pneumatic tire according to the invention;

FIG. 5 is an enlarged view of a main part of a bead portion in the tireof FIG. 4;

FIG. 6 is a diagrammatically left-half section view of a secondembodiment of the pneumatic tire according to the invention;

FIG. 7 is an enlarged view of a bead core shown in FIG. 4;

FIG. 8 is a diagrammatically left-half section view of a thirdembodiment of the pneumatic tire according to the invention;

FIGS. 9a and 9 b are diagrammatically left-half section views of fourthand fifth embodiments of the pneumatic tire according to the invention,respectively;

FIGS. 10a and 10 b are diagrammatically left-half section views of sixthand seventh embodiments of the pneumatic tire according to theinvention, respectively;

FIG. 11 is a diagrammatically left-half section view of an eighthembodiment of the pneumatic tire according to the invention;

FIGS. 12a and 12 b are diagrammatically left-half section views of ninthand tenth embodiments of the pneumatic tire according to the invention,respectively;

FIG. 13 is a diagrammatically left-half section view of an eleventhembodiment of the pneumatic tire according to the invention;

FIG. 14 is a diagrammatically left-half section view of anotherconventional pneumatic tire;

FIG. 15 is a diagrammatically left-half section view of a twelfthembodiment of the pneumatic tire according to the invention;

FIG. 16 is a diagrammatically left-half section view of a thirteenthembodiment of the pneumatic tire according to the invention;

FIG. 17 is diagrammatically left-half section view illustrating adeformation behavior of the tire shown in FIG. 16;

FIG. 18 is a diagrammatically left-half section view of a fourteenthembodiment of the pneumatic tire according to the invention;

FIG. 19 is a diagrammatically left-half section view of a fifteenthembodiment of the pneumatic tire according to the invention:

FIG. 20 is a schematically plan view illustrating an embodiment of thetire manufacturing apparatus according to the invention;

FIGS. 21a and 21 b are a side view and a front view partly shown insection of an embodiment of the carcass band bending apparatus used inthe invention, respectively;

FIG. 22 is a perspective view illustrating an action of the apparatusshown in FIG. 21;

FIG. 23 is a front view illustrating another embodiment of the carcassband bending apparatus used in the invention;

FIGS. 24a to 24 e are block diagrams illustrating the manufacturingsteps of the apparatus shown in FIG. 20;

FIGS. 25a and 25 b are block diagrams illustrating action steps of abead setter;

FIG. 26 is a diagrammatically enlarged section view illustrating astitching state;

FIG. 27 is a diagrammatically section view illustrating a structure of abead portion in a product tire after vulcanization;

FIG. 28 is a schematically plan view illustrating another embodiment ofthe tire manufacturing apparatus according to the invention;

FIGS. 29a to 29 e are block diagrams illustrating the manufacturingsteps of the apparatus shown in FIG. 28;

FIGS. 30a and 30 b are diagrammatically section views of bead portion ina new tire and last use stage for illustrating amount of permanent setin fatigue of bead portion;

FIG. 31 is a graph showing a relation between thickness of rubber layerand index of bead portion durability; and

FIG. 32 is a graph showing a relation between protruding length ofrubber layer from bead portion reinforcing layer and index of beadportion durability.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 4 is shown a first embodiment of the pneumatic tire according tothe invention and FIG. 5 shows an enlarged view of a main part of a beadportion in the tire shown in FIG. 4, wherein numeral 11 is a treadportion, numeral 12 a sidewall portion continuously connecting from anend of the tread portion 11, numeral 13 a bead portion continuing froman inside of the sidewall portion 12 in a radial direction of the tire,and numeral 14 a bead core embedded in the bead portion 13 and having ahexagonal shape at a section thereof in the radial direction.

In the illustrated embodiment, a carcass ply 15 containing a steelcord(s) arranged substantially at a cord angle of 90° with respect to anequatorial plane of the tire and having a tenacity of 80-300 kgf,preferably 100-180 kgf is toroidally extended from the tread portion 11through the sidewall portion 12 to the bead portion 13 and turned aroundthe bead core 14 from an inside toward an outside in the radialdirection of the tire.

As the turning embodiment, there are a case that the carcass ply isturned from the inside toward the outside in the widthwise direction ofthe tire as shown in FIG. 4, and a case that the carcass ply is turnedfrom the outside toward the inside in the widthwise direction of thetire as shown in FIG. 6. In both the cases, a turnup portion 15 b of thecarcass ply 15 has a wrap part 17 wrapping on a peripheral face of thebead core 14 therealong.

In the wrap part 17 shown in FIGS. 4 and 6, three plastic deformationregions p₁, p₂, p₃ corresponding to radial section profile of the beadcore 14 are previously formed in a portion of the carcass ply 15corresponding to the warp part 17 prior to the winding of the carcassply 15 around the bead core 14 and a top end portion of the carcass plyis particularly wrapped on the bead core 14 sufficiently near to theperipheral face thereof and more accurately followed thereto by theaction of such plastic deformation regions.

And also, the wrap part 17 is extended along the peripheral face of thebead core 14 over a half periphery of the sectional profile of the beadcore 14, for example, a half periphery of the bead core 14 located at aside of a bead base 13 a. In the illustrated embodiment of FIG. 4, anouter end 17 a of the warp part 17 is located inward over a position Qof an outer circumferential edge of the bead core 14 in the widthwisedirection of the tire at a state of mounting the tire onto a rim R underan inflation of a maximum air pressure.

Moreover, numeral 18 is a wire chafer arranged around the bead core 14and circumscribed with the carcass ply 15, which may be used ifnecessary.

In the tire having the above structure, the wrap part 17 is formed onthe turnup portion 15 b, so that the pulling-out of the carcass ply cordis effectively prevented and also separation failure of the turnupportion 15 b can effectively be prevented under the action of the beadcore 14 and the rim R.

As a natural consequence that the pulling-out of the carcass ply cord iseffectively prevented as mentioned above, even when the wire chafer 18is used as a necessary constructional member, the outer end of the wirechafer 18 in the radial direction can sufficiently be located toward aninner peripheral side in the radial direction, whereby the deformationamount of the outer end and its neighborhood is decreased to effectivelyremove a fear of causing separation failure at the outer end of the wirechafer.

In order to ensure such effects of the pneumatic tire, as the section ofthe bead core 14 in FIG. 4 is enlargedly shown in FIG. 7, it isfavorable that the end 17 a of the wrap part 17 is located on any sideamong three sides a, b, c separated from the bead base 13 a. Morepreferably, the position of the end 17 a is within a range from aposition corresponding to ⅔ of a length L₁ of the side a to a positioncorresponding to ⅔ of a length L₂ of the side b including an intersectposition Q between the side a and the side b.

In the illustrated embodiments of FIGS. 4 and 6, the wrap part 17 isinterposed between the bead core 14 and the bead filler 19, whereby therestraining force to the wrap part 17 is enhanced to more develop theabove effects.

Moreover, when the wrap part 17 is interposed as mentioned above, if theturnup portion 15 b has a protrusion end zone 20 extending outward alonga main body 15 a of the carcass ply 15 in the radial direction of thetire and separated away from the bead core 14 as shown in FIG. 8, theprotrusion end zone 20 may be released from the above interposed regionbetween the bead core and the bead filler.

In case of the turnup portion 15 b having the protrusion end zone 20, itis favorable to locate an end 20 a of the protrusion end zone 20 inwardfrom an outer peripheral edge of the contact region ct of the beadportion 13 with the rim flange Rf in the radial direction of the tireunder conditions of maximum air pressure and maximum load capacity,whereby the deformation of the end 20 a and its neighborhood during therunning of the tire under loading can effectively be restrained by therim flange Rf.

Although the above embodiments are described by forming three plasticdeformation regions p₁, p₂, p₃ in the wrap part 17, the number of theplastic deformation regions can be properly changed, if necessary. Forexample, the formation of one plastic deformation region is shown inFIG. 9a, and the formation of two plastic deformation regions is shownin FIG. 9b, and the formation of four plastic deformation regions isshown in FIGS. 10a and 10 b, respectively.

In case of the four plastic deformation regions p₁, p₂, p₃ and p₄, whenan end 17 a of the wrap part 17 is interposed between the main body 15 aof the carcass ply 15 and the bead core 14 as shown in FIG. 10a, therestraint to the wrap part 17 can strongly be increased, while when theend portion of the wrap part 17 is folded outward in the widthwisedirection of the tire to form a fold zone 21 as shown in FIG. 10b, thereis not caused tensile strain at the end portion of the carcass ply andhence the pulling-out of the carcass ply cord and the occurrence ofcrack hardly occur.

In the pneumatic tires having the aforementioned structure, the wrappart 17 wrapping on the bead core 14 along the peripheral face thereofis formed in the turnup portion 15 b of the carcass ply 15, whereby theoccurrence of separation failure at the wrap part 17 and hence theturnup portion 15 b is prevented and also the pulling-out of the carcassply cord can be prevented. And also, the number of the reinforcinglayers in the bead portion 13 can advantageously be reduced to controlthe heat generation of the bead portion 13 and reduce the tire weightand increase the tire productivity.

Furthermore, the occurrence of separation failure at an outer end of thewire chafer 18 in the radial direction can sufficiently be preventedbecause the height of the wire chafer in the radial direction can be setto a lower level based on the fact that there is no fear of causing thepulling-out of the carcass ply cord.

In the tire of FIGS. 4 and 5, when the displacement d of the point Xchanged from the deflate state to the inflate state is not more than 3mm as measured at the section in widthwise direction of the tire, thepermanent set in fatigue of the bead portion can considerably bedecreased.

Furthermore, the radius of curvature R0 in the point X at the deflatestate is favorable to satisfy R₀<2H, preferably R₀<H. Thus, thepermanent set in fatigue of the bead portion can be more decreased.

In case of R₀<H, the pushing amount (i.e. displacement d) of the beadportion at the inflate state can be made zero or the bead portion can bedeformed (recessed) in a direction opposite to the pushing direction,whereby the permanent set in fatigue of the bead portion can be morecontrolled.

As shown in FIG. 11, a rubber reinforcing member 16 may be disposed atan inner surface side of the main body 15 a of the carcass ply 15 over arange of from the bead portion 13 to the sidewall portion 12. In thiscase, the radius of curvature R₀ of the carcass ply 15 in the point X atthe deflate state can be made small, whereby the pushing deformation ofthe carcass outward in the widthwise direction of the tire can becontrolled at the inflate state.

The rubber reinforcing member 16 is favorable to have a modulus at 100%elongation of 1-3 MPa and is preferably disposed from a positiondistanced by 10 mm upward from the bead core in the radial direction upto a neighborhood of a maximum width position of the sidewall portion.

As the bead portion structure, there may be taken a structure that thewrap part 17 is wrapped on the bead core 4 formed by embedding a platebead 22 in a hard rubber 23 as shown in FIG. 12a, and a structure thatthe wrap part 17 is wrapped on the bead core 4 consisting of a roundbead 24 as shown in FIG. 12b in addition to the structure that the wrappart 17 is wrapped on the bead core 4 having a hexagonal section asshown in FIG. 4.

In FIG. 13 is diagrammatically shown the other embodiment of the heavyduty pneumatic tire according to the invention, wherein numeral 31 is abead core having a hexagonal shape at its section, numeral 32 at leastone carcass ply containing steel cords therein and having a wrap partwrapped on the bead core 31 at five plastic deformation regions 32 a, 32b, 32 c, 32 d, 32 e corresponding to corners of the bead core. And also,numeral 33 is a bead filler, numeral 34 a bead portion reinforcing layerof steel cords arranged along an outer surface of the carcass ply 32,numeral 35 a rubber layer disposed between the bead filler 33 and thebead portion reinforcing layer 34, and numeral 36 a side rubberconstituting a sidewall portion of the tire.

On the other hand, an example of the bead portion structure in theconventional heavy duty pneumatic tire is diagrammatically shown in FIG.14. When such a conventional tire is mounted onto a heavy duty vehiclerecently used by increasing an output and tire weight, a load in thebead portion becomes large and it tends to extremely shorten the life ofthe bead portion due to the occurrence of separation failure of thecarcass ply in the bead portion. In the tire having the structure shownin FIG. 13, however, strain in the end portion of the carcass ply 32 andthe end portion of the bead portion reinforcing layer 34 can bedecreased and hence the separation failure hardly occurs and thedurability of the bead portion is improved.

In FIG. 15 is diagrammatically shown a still further embodiment of theheavy duty pneumatic tire according to the invention, which is amodified embodiment of the tire shown in FIG. 13. That is, the beadfiller 33 is comprised of a main rubber stock 33 a having a JIS hardnessof 60-80° and a sub-rubber stock 33 b having a JIS hardness of not lessthan 80°. By adopting such a bead filler 33 can be controlled thedeformation of the bead portion as a whole in the circumferentialdirection to reduce shearing strain applied to the bead portionreinforcing layer 34.

In FIG. 16 is diagrammatically and partly shown a yet further embodimentof the heavy duty pneumatic radial tire according to the invention,which has the same structure as the tire shown in FIG. 4 except that arecess zone 40 is formed in an outer surface of a part of the beadportion 13 located inward from a position PW of a maximum tire width ata radial section of the tire. Moreover, FIG. 16 shows a state under noload.

The recess zone 40 is a portion forming a space between the outersurface of the bead portion and a plane H contacting with the outersurface at two points (shown by a phantom line) as shown in FIG. 16.Moreover, the recess zone 40 has substantially an arc shape, a curvaturecenter of which is located outside the tire at the radial section of thetire.

When the tire of FIG. 16 is mounted onto the recommended rim R andsubjected to the maximum load under the maximum air pressure, as shownby a solid line in FIG. 17, a point of the outer surface of the beadportion 13 separated from the rim flange Rf is an alienation point P,and a bisector dividing the bead portion into two parts at thealienation point P is L1 (shown by a dot-dash line), and a line passingthrough the alienation point P and perpendicular to the bisector L1 asshown in FIG. 16 is L2, and a line passing through a center B_(C) of thebead core 14 and parallel to the normal line L2 is L3, and a thicknessof the bead portion on the normal line L2 is W_(P), and a thickness ofthe bead portion on the parallel line L3 (hereinafter called as maximumbead portion width) is W_(M).

In the tire of FIG. 16, it is favorable that the rubber gauge T(distance from the steel cord in the carcass ply 15 to the outer profileof the tire) in a region ranging outward from the position P₁corresponding to 1.8 times the maximum bead portion width W_(M) locatedfrom the position of the nominal diameter of the rim flange Rf in theradial direction of the tire to the position P_(W) of the maximum tirewidth (Wmax is a maximum tire width in FIG. 16) is made substantiallyequal to the rubber gauge T_(W) (distance from the steel cord in thecarcass ply to the outer surface of the tire) at the position P_(W) ofthe maximum tire width (the term “substantially equal” used herein means0.7-1.3 times the rubber gauge T_(W) at the position P_(W) of themaximum tire width).

In the illustrated embodiment, a ratio of thickness of bead portionW_(P) on the normal line L2 to maximum bead portion thickness W_(M) ofthe bead portion 13 is set to 0.88.

In the illustrated tire, the rubber gauge of the bead portion isdecreased by forming the recess zone 40 in the outer surface of the beadportion 13, so that heat build-up of the bead portion 13 is reducedduring the running of the tire under loading and hence the bead portiondurability can largely be improved.

Moreover, if the rubber gauge T located outward from the position P₁ inthe radial direction is not substantially equal to the rubber gaugeT_(W) at the position P_(W), or if the rubber gauge T is thinner thanthe rubber gauge T_(W) (T is less than 0.7 T_(W)), the portion near tothe bead core 14 is too thin and the bending deformation of the beadportion concentrates near to the bead core 14 and hence it is apt tocause the crack at the outer surface of the bead portion due to theconcentration of strain in the outer surface of the bead portion near tothe bead core.

In FIG. 18 is shown a modified embodiment of the tire shown in FIG. 16,wherein the depth of the recess zone 40 is deeper than that of FIG. 16and the ratio of thickness W_(P) of bead portion on the normal line L2to maximum bead portion thickness W_(M) is set to 0.85.

In FIG. 19 is shown another modified embodiment of the tire shown inFIG. 16, wherein the recess zone 40 is formed outward from thealienation point P of the bead portion 13 in the radial direction, andthe outer surface of the bead portion 13 located inward from the recesszone 40 in the radial direction has an approximately arc shape, acurvature center of which being located at the inside of the tire, andthe ratio of thickness W_(P) of bead portion on the normal line L2 tomaximum bead portion thickness W_(M) is set to 0.92. In this case, thefall-down deformation of the bead portion 13 under loading can be moresuppressed as compared with the cases of FIGS. 16 and 18 and hence heatbuild-up can be more controlled.

In FIG. 21 is shown an embodiment of the apparatus for manufacturing apneumatic tire according to the invention, wherein numeral 50 is amotor, numeral 52 a carcass band drum attached to an output shaft of themotor 50. The carcass band drum 52 is added with a shaping meansmentioned later and mainly acts to laminate and wind tire constructionalmembers such as an innerliner, a carcass ply and the like fed from aservicer 54 onto a peripheral surface of the carcass band.

Moreover, a belt-tread band drum (hereinafter referred to as BT drum) 56is attached to the output shaft of the motor, and a belt and a tread fedfrom a service 58 are successively laminated and wound by the BT drum56.

In the illustrated embodiment, an O-ring 60 and a pair of bead setters62 are successively separated from the carcass band drum 52 at a sideopposite to the motor 50 and arranged with respect to the carcass banddrum 52. In this case, the O-ring 60 stands at a state of holding abelt-tread band (hereinafter referred to as BT band) formed on the BTdrum 56 for a period up to joining and acts to transport the BT band toan outer peripheral position of the carcass band drum 52 at the joiningof the BT band. The bead setter 62 acts to insert a ring-shaped beadcore previously held at the bead setter into an inside of a bend endportion of the cylindrical carcass band as mentioned later.

In the vicinity of the carcass band drum 52 are arranged a carcass bandbending apparatus 64 for subjecting each end portion of the cylindricalcarcass band formed on the drum 52 to a given bending work over fullperiphery of the carcass band, and stitcher rolls 66 for sufficientlypressing the bend end portion of the cylindrical carcass band to thebead core inserted into the inside thereof.

As shown in FIGS. 21a and 21 b, the carcass band bending apparatus 64can be constituted by two arm members 66, 68 hinged to each other, ahandled clamp screw 70 capable of properly adjusting a relative anglebetween the arm members, shafts 72 a, 72 b passing through free endportions of the arm members 66, 68 in their thickness directions andextending in parallel to each other and rotatably supporting these freeend portions, a shaft-shaped member 76 provided with an annular groove74 and attached to either one of the shafts (72 a) and a disc-shapedmember 78 attached to the other shaft (72 b) so as to put at leastperipheral part into the annular groove 74 and having a shape similar toa counter of an abacus in the illustrated embodiment. Preferably, aplurality of fine grooves extending in an axial direction are formed ona surface of the shaft-shaped member 76 other than the annular groove 74by subjecting such a surface to knurling work for enhancing frictionforce to the cylindrical carcass band.

The carcass band bending apparatus can be actuated by connecting arotation driving means (not shown) to at least one of the shafts (shaft72 a in the illustrated embodiment) and driving the shaft 72 a at astate of sandwiching a given position of an end portion of thecylindrical carcass band between the shaft-shaped member 76 and thedisc-shaped member 78 at a given force.

This is illustrated in FIG. 22, wherein a given position of an endportion of a cylindrical carcass band 80 is pushed into an annulargroove 74 of the shaft-shaped member 76 through the disc-shaped member78 by screwing of the clamp screw 70 and the shaft 72 a and hence theshaft-shaped member 76 is rotated by the actuation of a motor 82connected to the shaft 72 a, whereby the shaft-shaped member 76 isrelatively moved to the cylindrical carcass band 80 in a directionopposite to the rotating direction based on friction force to thecarcass band 80, while the disc-shaped member 78 is rotated in the aboverelative moving direction by the friction force to the carcass band 80while maintaining a state of pushing the carcass band 80 into theannular groove 74. As a result, the end portion of the carcass band 80is subjected to a required bending formation over its full periphery.

In this case, the carcass band bending apparatus 64 can be moved to aposition-specified cylindrical carcass band 80, or only the cylindricalcarcass band 80 can be rotated, or both these cases may be combined.

In the bending apparatus 64, the shaft-shaped member 76 can be contactedwith an outer peripheral surface of the carcass band 80 and thedisc-shaped member 78 can be contacted with an inner peripheral surfaceof the carcass band 80 in relation to the bending direction of the endportion of the carcass band 80.

In FIG. 23 is shown another embodiment of the bending apparatus, whereinthree annular grooves 74 are formed in the shaft-shaped member 76 atgiven intervals in the axial direction thereof and three disc-shapedmembers 78 are arranged side by side on its axial line at positionscorresponding to the annular grooves 74.

According to the illustrated embodiment of FIG. 23, three bent portionscan simultaneously be formed on the end portion of the carcass band 80in the same directions, so that the bending formation efficiency can bethree times that of the case shown in FIGS. 21 and 22.

The manufacturing method according to the invention using the abovemanufacturing apparatus will be described with reference to FIG. 24. Atfirst, an innerliner, a sidewall, a wire chafer and the like fed fromthe servicer 54 are wound around the carcass band drum 52 as shown inFIG. 24a and then a carcass ply fed from the servicer 54 is laminatedwound around the carcass band drum to form a cylindrical carcass band 80as shown in FIG. 24b.

In this case, it is favorable that each end portion of the cylindricalcarcass band 80 is laminated through a releasing member, for example, aplastic sheet 82 for facilitating the putting operation through thebending apparatus 64 in the bending formation work.

Thereafter, a pair of bead setters 62 shown in FIG. 20 are moved onto acentral portion of the carcass band drum 52 and hence the cylindricalcarcass band 80 at a state of magnetically adsorbing a ring-shaped beadcore 86 on a bead holder 84 as shown in FIG. 24c, at where a givenposition of each end portion of the cylindrical carcass band 80 isputted between the shaft-shaped member 76 and the disc-shaped member 78in the carcass band bending apparatus 64 at a given force and thecylindrical carcass band 80 is subjected to the required bendingformation work over its full periphery under the aforementioned actionof the bending apparatus 64.

In FIG. 24d is shown a state that bent end portions 88 directing outwardin the radial direction are formed on both end portions of the carcassband 80 by simultaneously forming three bending work parts on each ofthe shaft-shaped member 76 and the disc-shaped member 78 of bendingapparatus 64 in the axial direction of the carcass band 80 as shown inFIG. 23.

In such a bending apparatus 64, the insertion of the shaft-shaped member76 into the inner peripheral side of the carcass band 80 can easily becarried out by maintaining the end portion of the carcass band 80through the plastic sheet 82 at a non-joined state to the membersarranged in the inner peripheral side. Therefore, the plastic sheet 82may properly be removed at a subsequent stage.

Moreover, local outward pushing of the cylindrical carcass band 80 inthe radial direction due to the insertion of the shaft-shaped member 76into the inner peripheral side of the carcass band 80 on the carcassband drum 52 can be eliminated by enlarging the carcass band 80 over itsfull periphery through the operation of the bead lock mentioned later.

The bead core 86 held by the bead holder 84 is inserted into an insideof a bent end portion 88 formed in the cylindrical carcass band 80 underthe action of the bead setter 62. This is shown in FIGS. 25a and 25 b.At first, hooks of hook-shaped enlarging members 90 in the bead setter62 are engaged with an end of the bend end portion 88 at pluralpositions in the circumferential direction and then the hooks are movedin a direction of opening the end of the bend end portion 88 or outwardin the axial direction of the carcass band 80 in FIG. 25a to deform thebend end portion 88 in its elastic zone. Thereafter, the bead holder 84and hence the bead core 86 adsorbed on the outer surface thereof ismoved to the axial end direction of the carcass band 80 whilemaintaining such a deformed state to locate the bead core 86 at theinside of the bend end portion 88. Then, the engagement of thehook-shaped enlarging member 90 with the bent end portion 88 is releasedto return the bent end portion 88 into the original bending work shape.

In this case, the returning into the original bending work shape may beobstructed in accordance with the shape, size and the like of the bentend portion 88 when the bent end portion 88 is closed to the peripheralface of the bead core 86.

Thereafter, the bead lock 92 arranged in the carcass band drum 52 isactuated outward in the radial direction to hold the bead core 86 insidethe bent end portion 88 from its inner peripheral side at pluralpositions in the circumferential direction, whereby it is made possibleto separate the bead core 86 from the bead holder 84 magneticallyadsorbing the bead core 86.

Moreover, since the bead lock 92 restrains the relative movement of thebead core 86 to a direction crossing to the axial line of the carcassband drum, but allows the movement in the axial lien direction, ashaping means incorporated in the carcass band drum 52, for example, abladder 94 is actuated to toroidally expand the cylindrical carcass band80 under the movement of the bead lock 92 and the bead core 86approaching to each other as shown in FIG. 24e.

After the shape of the carcass band 80 including the bent end portion 88is sufficiently closed to a shape of a built green tire and hence aproduct tire by toroidally expanding the carcass band 80, as enlargedlyshown in FIG. 26, the bent end portion 88 is subjected to stitchingthrough stitcher roll 66 to more press the whole of the bent end portion88 onto the peripheral surface of the bead core 86, whereby the bent endportion 88 is accurately wound around the peripheral surface of the beadcore 86 to ensure a high tensile strength in the carcass band 80.

Prior to the expansion deformation of the carcass band 80, the O-ring 60shown in FIG. 20 is previously moved to a given position on the outerperiphery of the carcass band drum 52 at a state of holding the BT band,whereby the BT band can be joined to the outer peripheral surface of thecarcass band 80 accompanied with the expansion deformation of thecarcass band.

After the completion of a series of the above works, the conventionalgeneral works are continued up to the completion of green tire building.

In FIG. 27 is shown an embodiment of a bead portion structure after thethus obtained green tire is subjected to tire building throughvulcanization, from which it is clear that the bent end portion 88 isaccurately wound around the bead core 23 based on the fact that the bentend portion is previously formed in the carcass band 80 accompanied withthe plastic deformation and such a winding posture can surely bemaintained up to the completion of the tire building throughvulcanization.

In FIG. 28 is shown another embodiment of the tire manufacturingapparatus according to the invention, wherein numeral 100 is a carcassband drum conducting only the formation of the cylindrical carcass band,and numeral 102 a servicer feeding a carcass ply to the carcass banddrum 100.

Numeral 104 is a transporting means of the cylindrical carcass band 80,which acts to receive the cylindrical band 80 formed on the carcass banddrum 100 and transport it into a shaping drum mentioned later. And also,the transporting means 104 acts to form the bend end portion 88 of thecarcass band 80 together with the carcass band bending apparatus 64 andthe bead setter 62 (not shown) attached thereto and insert the bead core86 into the inside of the bent end portion 88.

Numeral 106 is a shaping drum provided with a shaping means. In theshaping drum 106, an innerliner, a sidewall, a wire chafer and the likeare wound and laminated and shaped together with the carcass band 80.

Moreover, the BT drum 56, the O-ring 60 and so on have substantially thesame actions as mentioned above.

In the manufacture of the tire using the above apparatus, the carcassply fed from the servicer 102 is wound around the carcass band drum 100to form the cylindrical carcass band 80 as shown in FIG. 29a, while thecarcass band 80 is received by the transporting means 104, at where thebent end portion 88 is formed on the end portion of the carcass band 80by the carcass band bending apparatus 64 as shown in FIG. 29b and thebead core 86 is inserted into the inside of the bent end portion 88 bythe bead setters 62.

On the other hand, the innerliner, sidewall, wire chafer and so on arepreviously wound and shaped on the shaping drum 106 as shown in FIG.29c, and the carcass band 80 including the bead core 86 as mentionedabove is transported and positioned onto an outer peripheral sidethereof by the transporting means 104 as shown in FIG. 29d, andthereafter the shaping drum 106 is enlarged to a given outer diameterenough to hold the cylindrical carcass band 80 from the inner peripheralside.

Thereafter, the bead lock 92 is actuated to hold the bead core 86 fromits inner peripheral side, while a bladder 94 as a shaping means isexpanded to toroidally expand and deform the carcass band 80 and thebent end portion 88 is subjected to stitching through stitcher rolls 66under such a state.

In this case, the BT band formed by the BT drum 56 and held by theO-ring 60 is positioned at the outer peripheral side of the carcass band80 prior to the expansion deformation of the carcass band 80, wherebythe BT band is joined to the outer peripheral surface of the carcassband 80 accompanied with the expansion deformation of the carcass band.

In the pneumatic tire manufactured through the above steps, the bent endportion 88 accurately wound on the peripheral surface of the bead core86 is previously formed on the end portion of the cylindrical carcassband 80, so that the winding posture as shown in FIG. 27 can surely bemaintained even after the completion of the tire building throughvulcanization.

The following examples are given in illustration of the invention andare not intended as limitations thereof.

EXAMPLES 1-9, CONVENTIONAL EXAMPLES 1-2

There are provided pneumatic radial tires for truck and bus having atire size of 285/60R22.5, which are mounted onto a rim of 9.00×2.5,respectively. Then, the pulling-out of carcass ply cord, durabilitythrough drum test, heat build-up temperature of bead portion and tireweight are measured to obtain results as shown in Table 1.

These tires have a bead portion structure and details thereof as shownin Table 1, respectively.

The pulling-out of carcass ply cord is evaluated by three stages ofsymbol ⊚ (no pulling-out), symbol ◯ (moving a part of carcass ply cordsbut not pulling out) and symbol X (occurrence of pulling-out) after thepresence or absence of the cord pulling-out is examined by supplyingwater pressure of 60 kgf/cm² to the inside of the tire mounted onto therim.

The durability on drum is evaluated by a drum test that the tire mountedonto the recommended rim and inflated under the maximum air pressure isrun on a drum under a load corresponding to 2 times the maximum loadcapacity to measure a running distance until the running is impossibledue to the occurrence of bead portion trouble (separation at the turnupend of carcass ply or at the end of wire chafer), crack in bead filleror the like and represented by an index on the basis that ConventionalExample 1 is 100, wherein the larger the index value, the better thedurability.

The heat build-up temperature of bead portion is evaluated by measuringa temperature near to the turnup end of the carcass ply by means of athermocouple previously embedded in the vicinity of the turnup end after2 hours in the running on the drum and represented by an index on thebasis that Conventional Example 1 is 100, wherein the smaller the indexvalue, the better the property.

Further, the tire weight is represented by an index on the basis thatConventional Example 1 is 100, wherein the smaller the index value, thelighter the weight.

TABLE 1 Conven- Conven- Example Example Example Example Example ExampleExample Example Example tional tional 1 2 3 4 5 6 7 8 9 Example 1Example 2 Bead portion FIG. 4 FIG. 6 FIG. 9a FIG. 9b FIG. 10a FIG. 10bFIG. 8 FIG. 12a FIG. 12b FIG. 1a FIG. 1b structure Number of car-  1  1 1  1  1  1  1  1  1  1  1 cass plies Structure of 1 × 27 × 1 × 12 × 1 ×27 × 1 × 27 × 1 × 27 × 1 × 12 × 1 × 12 × 1 × 12 × 1 × 12 × 1 × 12 × 1 ×12 × carcass ply 0.18 0.225 0.18 0.18 0.18 0.225 0.225 0.225 0.225 0.2250.225 cord Sectional shape of hexa- hexa- hexa- hexa- hexa- hexa- hexa-bead round hexa- hexa- bead core gonal gonal gonal gonal gonal gonalgonal plate + bead gonal gonal hard rubber Number of plastic  3  3  1  2 4  4  3 circle circle none none deformation formed formed regionsPulling-out ⊚ ◯ ◯ ◯ ⊚ ⊚ ⊚ ◯ ⊚ ⊚ ◯ of carcass ply cord Durability on 180140 120 140 180 160 140 130 140 100  90 drum (index) Heat build-up  85 80  85  85  85  90  90  80  85 100 110 temperature of bead portion(index) Tire weight  92  90  94  96  92  94  94  96  94 100 102 (index)

EXAMPLES 10-12, COMPARATIVE EXAMPLE 1

There are provided pneumatic radial tires for truck and bus having atire size of 285/60R22.5 as Examples 10-12. In these tires, the beadportion structure, number of carcass plies, structure of carcass plycord, sectional shape of bead core, number of plastic deformationregions, displacement d of point X from deflate state to inflate state(mm), radius of curvature R₀ at point X at deflate state (mm) andcontact pressure Pf of bead portion to rim at inflate state are shown inTable 2. Moreover, the contact pressure Pf is represented by an index onthe basis that Conventional Example 1 is 100.

For the comparison, there are provided a tire having a tire structureshown in FIG. 1 as Conventional Example 1, wherein the radius ofcurvature at point X at deflate state is indefinite (i.e. approximatelystraight line), and a tire having a tire structure shown in FIG. 4except that the displacement d exceeds 3 mm as Comparative Example 1.

Each of these tires is mounted onto a rim of 9.00×22.5 and then thepulling-out of carcass ply cord, durability through drum test, heatbuild-up temperature of bead portion and tire weight are measured in thesame manner as described in Example 1 and the amount of permanent set infatigue of bead portion is measured by the following test method toobtain results as shown in Table 2.

The amount of permanent set in fatigue of bead portion D (mm) as shownin FIG. 30b is measured after the tire mounted onto the rim as shown inFIG. 30a is inflated under a maximum air pressure and run on a drumrotating at a speed of 60 km/h under a load corresponding to 1.2 times amaximum load capacity over a distance of 100000 km, wherein the smallerthe numerical value, the better the property.

TABLE 2 Conventional Comparative Example 10 Example 11 Example 12Example 1 Example 1 Bead portion FIG. 4 FIG. 4 FIG. 11 FIG. 12correspond- structure ing to FIG. 4 Number of carcass 1 1 1 1 1 pliesStructure of carcass 1 × 27 × 0.18 1 × 27 × 0.18 1 × 27 × 0.18 1 × 12 ×0.225 1 × 27 × 0.18 ply cord Sectional shape of hexagonal hexagonalhexagonal hexagonal hexagonal bead cord Number of plastic 3 3 3 none 3deformation regions Displacement d of 2.8 1.0 0 6.0 4.5 point X*¹ (mm)Radius of curvature 250 140 80 ∞ 400 R₀ at point X*² (approximatelystraight) Contact pressure Pf 80 55 20 100 95 of bead portion to runPulling-out of carcass ⊚ ⊚ ⊚ ⊚ ⊚ ply cord Durability on drum 180 180 170100 180 (index) Heat build-up 75 70 80 100 85 temperature of beadportion (index) Tire weight (index) 88 86 88 100 92 Amount of 2.1 1.71.2 4.2 3.6 permanent set in fatigue of bead portion (mm) *¹change ofdeflate state to inflate state *²at deflate state

As seen from Table 2, the tires of Examples 10-12 are equal to or morethan the tire of Conventional Example 1 in the pulling-out of carcassply cord, durability on drum, heat build-up temperature of bead portionand amount of permanent set in fatigue of bead portion and the tireweight is largely reduced.

EXAMPLE 13

In this example, bead portion durability is measured with respect tothickness t₂ of rubber layer 35, thickness t₁ of bead portionreinforcing layer 34 and protruding length L_(P) of rubber layer 35 frombead portion reinforcing layer 34 shown in FIG. 13 to obtain results asshown in FIGS. 31 and 32. In this case, a drum test is carried out bymounting a test tire having a tire size of 285/60R22.5 onto a rim of9.0×22.5R and running on the drum at an internal pressure of 882 kPaunder a load of 49.0 N.

In FIG. 31, the bead portion durability is represented by an index onthe basis that the thickness t₁=0 of the bead portion reinforcing layer34 is 100. As seen from FIG. 31, the effect of improving the durabilityis developed when t₂ is not less than 0.3t₁, while when t₂ exceeds0.5t₁, the more improving effect is not observed and there is rather ademerit of increasing the production cost and the tire weight. As aresult, the thickness t₂ of the rubber layer 35 is restricted to0.3t₁≦t₂≦5t₁ in the invention.

In FIG. 32, the bead portion durability is represented by an index onthe basis that the protruding length L_(P)=0 mm is 100. As seen fromFIG. 32, when a part of the rubber layer 35 is protruded from the end ofthe bead portion reinforcing layer 34, the improving effect isdeveloped, while when the protruding length L_(P) exceeds 30 mm, theimproving effect is saturated and there is rather a demerit ofincreasing the production cost and the tire weight. As a result, theprotruding length L_(P) of the rubber layer 35 from the bead portionreinforcing layer 34 is 30 mm at maximum in the invention.

In this connection, there are provided a tire shown in FIG. 14 (JIShardness of A-portion: 82°, JIS hardness of C-portion: 38°, t₁: 1.0 mm),a tire shown in FIG. 13 (JIS hardness of A-portion: 82°, JIS hardness ofB-portion: 60°, JIS hardness of C-portion: 38°, t₁: 1.0 mm, t₂: 2.4 mm,L_(P): 28 mm) and a tire shown in FIG. 15 (JIS hardness of A-portion:63°, JIS hardness of B-portion: 38°, JIS hardness of C-portion: 71°, JIShardness of D-portion: 82°, t ₁: 1.0 mm, t₂: 2.4 mm, L_(P): 28 mm), atire size of which tires is 285/60R22.5. Each of these tires is mountedonto a rim of 9.0×22.5R and run on a drum at an internal pressure of 882kPa under a load of 49.0 kN to measure a distance until the running ismade impossible due to the occurrence of separation failure in the beadportion.

When the running distance is represented by an index on the basis thatthe conventional tire shown in FIG. 14 is 100, the index value of thetire shown in FIG. 13 is 125, and the index value of the tire shown inFIG. 15 is 135. From these facts, it has been confirmed that the beadportion durability is considerably improved in the tires according tothe invention.

EXAMPLES 14-16

There are provided four tires having a tire size of 285/60R22.5, whereina tire of Example 14 is a tire having a structure shown in FIG. 16, atire of Example 15 is a tire having a structure shown in FIG. 18, a tireof Example 16 is a tire having a structure shown in FIG. 19, and aconventional tire has a structure having no recess zone 40 and wrap part17 as shown in FIG. 1a.

In these tires, the carcass ply 15 is a rubberized ply containing steelcords of (1×3+9+15)×0.175 mm+1×0.15 mm arranged side by side at an endcount of 26 cords/5 cm (measured around the bead core) and extendingsubstantially in a radial direction. And also, the bead portionreinforcing layer 18 is a rubberized layer containing steel cords of(1×3+9+15)×0.175 mm+1×0.15 mm arranged side by side at an end count of21 cords/5 cm (measured around the bead core) and inclined at a cordangle of 60° with respect to the radial direction (measured at an outerend portion in the axial direction of the tire).

Moreover, the ratio W_(P)/W_(M) is 0.88 in the tire of Example 14, 0.85in the tire of Example 15, and 0.92 in the tire of Example 16,respectively.

Each of these tires inflated under an internal pressure of 900 kPa isrun on a steel drum having a radius of 1.7 m at a speed of 60 km/h undera load of 5200 kg to measure a running distance until the occurrence oftrouble in bead portion (separation failure). In this case, a measuringtemperature is 46° C.

The bead portion durability is evaluated by an index on the basis thatthe running distance until the occurrence of bead portion trouble in theconventional tire is 100, wherein the larger the index value, the betterthe durability. The results are shown in Table 3.

TABLE 3 Conventional tire Example 14 Example 15 Example 16 Bead portion100 120 127 138 durability (index)

As seen from Table 3, the bead portion durability in the tires ofExamples 14-16 is largely improved as compared with that of theconventional tire. This shows that the tire according to the inventionis suitable for use in a base tire for recapping. And also, the tire ofExample 16 is less in the fall-down deformation of the bead portionunder loading as compared with the tires of Examples 14 and 15 becausethe ratio W_(P)/W_(M) is set to a value larger than 0.9.

As mentioned above, according to the invention, the wrap part wrappingaround the bead core along the peripheral surface thereof is formed inthe turnup portion of the carcass ply, whereby the pulling-out of thecarcass ply cord and separation failure in the turnup portion of thecarcass ply can effectively be prevented and the bead portion durabilitycan largely be improved. And also, the heat build-up of the bead portionand the tire weight can advantageously be reduced.

And also, according to the invention, the bent end portion is formed onthe end portion of the cylindrical carcass band and the bead core isinserted into the bent end portion, whereby the bent end portion canaccurately be wound on the peripheral surface of the bead core even whencords having a large elastic restoring force such as steel cords and soon are used as a cord in the carcass ply and the winding posture cansurely be maintained even after the tire building through vulcanization.As a result, the separation failure at the turnup end of the carcass plyis sufficiently prevented and the fear of pulling out the cord of thecarcass ply can sufficiently be removed.

What is claimed is:
 1. A pneumatic tire comprising a carcass comprisedof at least one carcass ply containing a steel cord(s) arranged at acord angle of 70-90° with respect to an equatorial plane of the tire andtoroidally extending between a pair of bead cores and wrapped around thebead core from an inside toward an outside in a radial direction to forma turnup portion, the improvement wherein a wrap part wrapping on aperipheral face of the bead core therealong is formed in the turnupportion of the carcass ply, wherein a displacement (d) of a point Xchanged from a deflated state to an inflated state is not more than 3 mmas measured at a section in the widthwise direction of the tire, whereinX is an arbitrary point on a carcass line located in a region of thebead portion outward from a contact region with a rim flange at thedeflated state when the tire is mounted onto a recommended rim.
 2. Apneumatic tire according to claim 1, wherein the tire satisfies arelation of R₀<2H, preferably R₀<H when a radius of curvature of thecarcass line at the point X is R₀ and a section height of the tire is Hat the deflate state.